Cruising

Chartplotter Protocols Page 2

By Steve Henkind  Posted: Nov 20, 2008

A chartplotter can’t think for you. Chartplotters are sophisticated, but they don’t understand what they are displaying. A chartplotter will give you the distance and bearing to a waypoint, but it won’t comment on whether there are any hazards along the way (Fig. 2). While most navigators wouldn’t let such a blunder occur, it happens more often than you may think. For example, if you establish a safe waypoint but are then set off the rhumb line by current, the chartplotter may alert you to a significant cross-track error, but it won’t know, and therefore won’t tell you, that your present course is potentially dangerous (Fig. 3). In fact, the plotter might even suggest another dangerous course to get you back onto the track line. Technology is being developed that will address this problem, but it’s not yet available. Until it is, my suggestion is that you keep a paper chart handy so you can keep track of the big picture.

A shoal can move. It might be reassuring to see a nice electronic image of all the hazards surrounding you on the plotter: “Shoals ahead? No problem—all we need do is thread our way through them.” The problem is that shoals (especially ones that are made of sand) can move. If you’re transiting through such an area, you shouldn’t rely exclusively on a chartplotter to keep you clear of the bottom. This is the time to use as many additional navigational inputs as possible—visual observations, compass bearings, depth readings, and the like. And be sure you have installed the most current chart chips available.

Update your chips. This is essential because it’s not just shoals that can move. Buoys can be repositioned, numbers can be changed, and new hazards, such as, wrecks, might emerge. Most chip manufacturers have subscription update services. These can be cheaper than making individual chip purchases.

A chartplotter won’t display everything. No matter how current your chips are, don’t expect your plotter to display all the potential hazards around you—another boat for example.Sailors who previously wouldn’t go out in fog and other low-visibility situations are doing so now because they have a chartplotter. Although a chartplotter is a big help in these situations, you must also keep a sharp visual lookout.